The subject matter of the present invention essentially is an elastic and compressible printing element, this element constituting what is called a blanket which may be secured onto the surface of cylinders which are provided in the printing machines.
Most of the printing blankets presently used in the printing machines essentially comprise a lithographic layer allowing the transfer of information from the blanket-carrying cylinder onto a web of paper and a compressible structure consisting of a layer of cellular rubber placed in sandwich-like relationship between two fabric layers.
Now the compressibility of such a blanket, i.e. its possibility of becoming deformed under the effect of a force exerted by the machine upon the blanket-carrying cylinder bearing onto another blanket-carrying cylinder for instance remains limited. Therefore a relatively great force should be exerted upon the blanket and this force will result with time in a sagging of the blanket which will no longer recover its initial thickness and geometry. Moreover it should be noted that in the modern quick-operating printing machines heatings promoting the sagging of the blanket will occur and of course the quality of impression of the paper web passing between both blanket-carrying cylinders and the travelling of this web will be strongly affected.
Moreover with such blankets which are not very compressible and which generate high pressures for a given nip between both blanket-carrying cylinders there are substantial risks of shearing. More specifically the material which constitutes the blanket tends to move sidewise to form in a way protrusions which is highly harmful to the quality of impression of the web of paper and to the proper travelling of this web.
There has also been proposed in the document FR-A-2,461,596 a blanket essentially comprising a lithographic layer, a layer of cellular rubber and a stabilizing or base layer consisting of several layers of fabric bonded with neoprene.
Here again however such a blanket is likely to generate high pressures in the nip between both cylinders carrying the blankets whereas this should be avoided so as to not impair the structure of the blanket and such a blanket may also incur risks of shearing, i.e. of sidewise displacement of the material of the blanket which leads to the inconveniences mentioned above.